Electropiano with plural piezoelectric pickups on unitary acoustic rail



July 7, 1970 D. w. MARTIN ETAL 3.519,721

ELECTROPIANO WITH PLURAL PIEZOELECTRIC PICKUL ON UNITARY ACOUSTIC vRAIL med Maron 21. 196e IFIG.

53 www XM/ @mms United States Patent O 3,519,721 ELECTROPIANO WITH PLURAL PIEZOELECTRIC PICKUPS ON UNITARY ACOUSTIC RAIL Daniel W. Martin, Cincinnati, and John L. Stein, Hamilton, Ohio, assignors to D. H. Baldwin Company, Cincinnati, Ohio, a corporation of Ohio Filed Mar. 21, 1968, Ser. No. 714,888 Int. Cl. G10c 7/00; G10d 5/00; G10k 1]/00 U.S. Cl. 84--1.14 11 Claims ABSTRACT OF THE DISCLOSURE An electropiano employing as a transducer rail one or relatively few strips of U-shaped aluminum extrusion between the arms of which are located a plurality of piezoelectric transducer elements separated from one arm by resilient damping pads located above metallic shims. The total number of transducer elements is about 25% of the number of tones, the transducers not being individual to the strings, but being acoustically coupled t the strings through the extrusion or strip. The strip is supported between the strings and a layer of resilient damping material which is located directly on the plate of the electropiano, and is secured only against gross lateral movement relative to the plate so that longitudinal acoustic vibrations along the length of the strip and ilexural vibrations of the extrusion can occur. The transducer elements each have one electrode contacting an arm of the extrusion, which then provides a common electrical ground. The other electrode of each transducer contacts a conducting shim superimposed on an electrical insulating and acoustical damping pad. These shims are connected to a common lead, so that all the outputs of a group of transducers may be applied to a common terminal. Damping means are provided just beyond the tuned segments of the strings, to provide tone diminution simulating that of a true piano.

BACKGROUND OF THE INVENTION The term, electropiano, as used herein means an instrument having a string plate, an action whereby the strings may -be struck into vibration, but lacking a conventional bridge and soundboard, and having means whereby string vibrations may be converted into electrical pulsations, and these in turn into sound by means of a loudspeaker. Tones produced by an electropiano should closely resemble the tones of a conventional acoustical piano. Great difficulty has been experienced in achieving true piano tone quality in an electropiano, particularly because the bridge and soundboard of the acoustical piano strongly intercouple the strings of the instrument, and also control to a great degree the decay characteristics of the acoustical piano tones.

In an acoustical piano the strings are set into motion by the hammers of the action, which immediately after striking the strings are brought out of contact with them. Tone dimunition is controlled by several factors, including string length, string coupling, termination impedance, and damping by the termination material and structure. When the dampers of a mechano-acoustic piano are raised, by the action of the sustaining pedal, considerable interaction among the strings representing notes of different fundamental frequencies occurs. The interplay among the strings is extremely complex, involving the numerous modes of vibration of each string, and accordingly gives the tone of an acoustical piano a recognizable quality. If this quality is not achieved in an electropiano the latter is not an optimum instrument.

Among the patents in the eld which have sought to solve the problems above stated are:

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Benioff, #3,049,958, which concerns itself with the design of transducers for individual electropiano notes and the production of suitable damping effects. The solution suggested Was an improvement for individual tones but the damping and supporting structure used was at the expense of losing sympathetic vibrations in strings of adjacent and distant string groups. Neither did it adequately overcome the tendency for tones to run together when played in rapid sequence.

Martin and Ziegler application Ser. N0. 553,335, led May 27, 1966 and entitled Electropiano, shows solutions to these problems.

In the above instances and in various other electropianos it has been common to utilize a transducer for each string or group of strings producing a single note. The requirement of a transducer per note yields a relatively complex structure which is costly and difficult to keep in adjustment,

According to the present invention, a single cantilever transducer rail which can be fabricated, for example, by aluminum extrusion is utilized commonly for all the strings on the piano, although if desired for convenience in construction, two or conceivably three sections of such extrusions may be employed. In the latter case, the plurality is essentially both mechanically and electrically the same as the single extrusion. By utilizing a single transducer rail for all the notes of the piano far fewer transducer elements may be employed than the number of tones of the piano. For example, in an 88-key piano, it is feasible to employ 20 to 25 piezoelectric transducer elements. Because all of the transducer elements are mounted in a common rail which is fabricated of metal and which is acoustically and structurally highly transmissive, coupling among the strings exists inherently, and vibration occurring anywhere along the rail is transmitted therealong to other strings.

The extrusion itself can be shaped to provide an edge on which the tuned segments of the strings terminate. Immediately beyond the tuned segment of the string and conveniently mounted directly on the extrusion can be provided a damping means for each string. This damping means is in the form of a dead rubber or plastic element in contact with the strings. The damping effect depends somewhat upon size, shape, density and hardness of the material.

The damping material can be distributed in individual pieces or for convenience of installation can be a continuous strip. It can be displaced toward or away from the end of the tuned segment to increase or decrease the diminution rate in accordance with the tonal needs in different pitch ranges. For ease of manufacture it is better to have a shallow trench in the extruded shape in which to position the damping material optimally. The different thicknesses, Widths or diameters of the damping material are used to vary the damping rate in different ranges.

While the aforementioned method is ideal for adjusting fixed diminution rates for the strings of individual notes or ranges, it is also possible to provide easily within the same instrument, the option of either piano-like diminution rates or more sustained, organ-like tones, by an alternate mounting of the damping material. For this purpose the damping material is mounted on a special damper rod extending along adjacent to the transducer rail, with the rod mechanically biased by weight or spring to hold the damping material in contact with the string extensions for piano-like diminution rates. When more sustained tones are desired this rod is drawn away by pedal, manual or electrical control means, removing the damping material temporarily from contact with the string extensions.

The transducer rail provides better internote coupling and a more piano-like tone decay envelope if the rail is supported in a damped resilient manner relative to the rigid plate rather than being rigidly clamped to the plate.

This in some ways resembles the Martin and Ziegler application mentioned above, but differs from it in that the transducer elements are within the rail structure. (In the Martin-Ziegler invention the elements were in individual-note transducers mounted upon a solid rail supported in a damped resilient manner.)

The theory of the action of the transducer rail and its support can be summarized in four parts, as follows:

(l) The mechanical impedance match between the transducer rail and the string (at a termination of their tuned segments) must resemble that of a conventional piano bridge, so that the transition from more rapid initial decay rate (for a group of initially in-phase strings) to less rapid terminal decay rate (for strings later out of phase most of the time) is possible. This is achieved in the present invention by the combination of the cantilever profile, the resilience mechanically in series with the transducer elements, and the resilient support for the entire transducer rail relative to the rigid plate.

(2i) Moreover, at or near the termination of the tuned segments there must be additional mechanical damping to substitute for that of the wood in a conventional piano bridge, so that the overall tone diminution rate will be satisfactory. In the present invention this is provided by the damping material contacting the strings just beyond their terminations, either on the transducer rail or on a separate rod removable for special organ-like tonal effect.

(3) Furthermore, internote coupling must occur, as it does with a conventional bridge supported upon a vibratile board, so that when the dampers are lifted from all strings (or alternatively in some pianos from a group of bass strings only) there will be substantial sympathetic vibration from nearby strings having similar modal frequencies, and to a lesser degree for distant strings. In the present invention this coupling results primarily from direct transmission through the continuous cantilever, and secondarily by flexure of the entire transducer rail as a result of its resilient (rather than strictly rigid) support upon the plate.

(4) The tonal output of the transducer elements results from variable stress at audio frequencies between the faces of the elements. A fixed stress, provided by normal compression of the rail cantilever arm toward its base, secures the elements in place and insures that large amplitudes of vibration `will not loosen the elements even momentarily. The damping pads between the elements and the rail prevent the rail from presenting too high a mechanical impedance to strings crossing at the elements, and help to equalize the output of the element for all strings in the immediate vicinity of the element. Both these damping pads and the damping material between the transducer rail and the plate prevent impact sounds in the rail and plate from having excessive duration.

SUMMARY OF THE INVENTION An electropiano employing acousto-electro transducers smaller in number than the number of tones of the electropiano, the transducers being mounted identically in a continuous aluminum strip of U-shaped cross-section, the strip being so associated with the string plate of the electropiano that internote coupling and damping occur which closely imitate the string intercoupling and damping which normally exists in a mechanical piano, so that true piano tone is closely simulated. Each string is provided with a damping surface located just beyond its tuned segment, which causes the string tone decay with time to simulate the decay curve of a true piano string.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a View in side elevation of a first embodiment of the invention;

FIG. 2 is a View in plan of the system of FIG. 1;

FIG. 3 is a View in section taken on the line 3-3 of FIG. 2;

4 FIG. 4 is a view in section taken on the line 4-4 of FIG. 3;

FIG. 5 is a partial view in section of a modification of the systems of FIGS. 1-4, inclusive, indicating a mode of varying the diminution rate of string vibration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS String plate 10 supports a plurality of stretched piano strings 11 between anchor pins 12 and tuning pins 13. Each string passing over an agratfe means 14 adjacent the tuning pins 13, and over a transducer assembly 15 adjacent the anchor pins 12. When strings are referred to they may involve one string per note, especially in the bass range cf the piano, and three strings per note in the treble section. Or, as in the case in some electropianos, one string per note may be used throughout.

The transducer assembly 15 preferably comprises an elongated aluminum extrusion E, having a U-shape in transverse section, i.e., a base arm 16, a cantilever arm 17, and a short element 18 joining the base 16 to the cantilever arm 17 at one side only, leaving the remaining side of the extrusion open, as in the manner of a U lying on its side. A single extrusion may extend across all the strings, and acts as an agraife element therefor, the instrument containing no bridge or sounding board. The extrusion may be subsequently curved to conform to the desired layout of termination points, or the transducer rail may be cast into a curved shape initially.

The transducer assembly 15 has about 20-25 transducer elements 20 for an entire piano, assuming 88 notes. The transducer elements 20 are distributed along the extrusion E such that the loudness of each separate note is appropriate to the loudness of that note in an acoustical piano. In this respect, bringing a transducer element closer to a string enhances its output in response to striking of that string.

The transducers 20 are preferably ceramic piezoelectric elements, and are provided with silver electrodes, and operate in the thickness mode. The lower electrodes of the piezoelectric elements 20 all impinge on the -base arm 16, so that the transducer assembly provides a common ground for all the transducer elements. The upper electrodes of the piezoelectric elements 20 contact bronze shims 25, which in turn contact a layer of insulating rubber material 26, which is also acoustically damping. The shims are all connected together by a common lead 28, which proceeds to an output terminal 29. The base 16 rests on a layer of acoustic isolating material 30, eg., felt, which acoustically isolates assembly 15 from the string plate 10, and assures that ringing of the string plate will not be communicated to the transducer assembly unduly.

The transducer elements 20, when assembled in an instrument, are under sucient compression that ac signals are accurately transduced and that elements 20 are not loosened due to strong vibration.

Alternative types of transducer elements can be used within the U shaped transducer rail 15. For example the rail may be of soft magnetic material such as iron, and magnet coil transducers can be substituted for the ceramic elements 20 either with or without rubber dampers 26.

In order to locate the transducer assembly 15 with respect to the string plate lil, holes 31 are provided in the base 16, which are grommeted loosely as at 32, and t over pins 33 secured to the string plate. The cantilever arm 17 is thus left free, because the grommets are not rigid, to vibrate piezoelectric element 20, with respect /to the base 16, and also to convey the vibrations longitudinally along its length to unstruck strings, which are set into vibration and provide electrical signals at their own resonance frequencies to the output terminal 29. This action simulates the action of the conventional acoustical piano very closely, except that in an acoustical piano interstring coupling occurs primarily via a bridge and soundboard, and in the present invention interstring coupling `occurs via the transducer assembly. This also overcomes a defect which commonly is found in an electropiano, i.e., that the tonal decay characteristic is quite unlike that occurring in an acoustical piano. The latter has essentially a double rate of decay, involving a rapid rate of decay to a lower level, followed by a very slo-w rate of decay thereafter. Electropianos usually have had almost linear decay rates.

Also in accordance with the present invention a damper of dead rubber 40, in the form of a strip, or a separate piece of such material, one per string (or string group), is located under the strings, in contact therewith, just outside the tuned segment of the strings. A suitable location is on the cantilever element. To maintain the dead rubber damper 40 in position a depression 41 may be formed in the upper face of the cantilever 17, to which the damper 40 conforms generally in shape. This damping action simulates the string damping by the wood of the conventional bridge right at the termination of the tuned segments of the strings. `If dampers 40 are right at the agraife edge of the cantilever or along the tuned segments the damping is abrupt and more difficult to control.

In FIG. 5 is illustrated a modification of the system of FIG. 3, wherein the dampers 40 are mounted on a movable rod 45, so that they may be separated from and moved into contact with the strings 11, or so that adjustable pressures against the strings may be achieved. This provides variations from conventional piano tonal diminution rates.

While We have described and illustrated one specific embodiment of the invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true scope and spirit of the invention as defined in the appended claims.

What is claimed is:

1. An electropiano comprising:

a plurality of strings extending between points of a string plate,

a transducer assembly extending transversely across and under said strings, said transducer assembly including a U-shaped extrusion extending under .a plurality of strings pertaining to a plurality of tones and having a base supported by said string plate and a cantilever arm on which said strings rest,

a plurality of piezoelectric elements secured in the space between the base and cantilever arm of said transducer assembly,

said extrusion being acoustically conducting along its length to intercouple said strings, and

means located under said base to acoustically isolate said piezoelectric elements from said string plate.

2. The claim according to claim 1 wherein is provided acoustic damping means secured between said strings and cantilever arm at points of said strings outside the tuned segments of said strings.

3. The claim according to claim 2 wherein said damping means consists of resilient rubber-like material.

4. The claim according to claim 1 wherein the number of said transducer elements is no more than half the number of said tones.

5. A string termination member for a stringed instrument, comprising:

an extended rail of U-shaped cross-section having a base arm and a cantilever arm extending parallel to said ibase arm and said cantilever arm,

said cantilever arm being a continuous element of high :acoustic transmittibility, whereby all points of said cantilever arm are acoustically coupled in a continuous path.

6. The claim according to claim S wherein said rail is a metallic extrusion.

7. The claim according to claim 5 wherein said cantilever arm participates in the mechano-electric transduction of the string vibrations.

8. The claim according to claim 7 wherein transducers :are enclosed within the rail.

9. The claim according to claim 8 wherein said transducers are ceramic piezoelectric compression elements.

10. The claim according to claim 5 wherein said string instrument scale includes:

nr notes having strings spaced along the length of said cantilever arm and wherein n transducer elements are secured along said extrusion in -coupled relation to said cantilever arm and located between said base arm and said cantilever arm, where n is less than m and m and n are both integers.

A transducer element for a stretched string, comprising:

a U-shaped metallic assembly having a base arm and a cantilever arm extending parallel to said base arm,

a piezoelectric element mounted between said base arm and said cantilever arm,

said stretched string being stretchable over said -cantilever arm,

an agraTe means extending from and integral with said cantilever arm, and

a mass of resilient acoustic damping material resting on said cantilever element adjacent said agraife means on the nonspeaking side of said string such that said string contacts said agraffe means and said damping material concurrently.

References Cited UNITED STATES PATENTS 2,222,057 11/1940 Benioff 84 l.16 2,334,744 ll/l943 ABeniolf 84-1.16 3,049,958 8/1962 Benioff 841.l6 3,396,284 8/1968 Scherer 3l0-8.3

WARREN F. RAY, Primary Examiner U.S. Cl. X.R. 

